A standard synthetic-resin shopping bag is formed by cutting a continuously arriving tube into a succession of short segments or blanks in such a manner that usually the leading and trailing edges of the blanks are sealed. These blanks are then stacked up and an edge is punched out to form a fill opening and a pair of handles, or the center of such a blank can be punched out to form two such bags. Stacking holes might also be punched in the bags so they can be dispensed conveniently from a carry pin.
The standard stacking apparatus comprises a pair of parallel wheels centered on a common horizontal axis that is perpendicular to the displacement direction of the arriving bag segments on an input conveyor. Each wheel has an array of radially projecting suction arms and the wheels are rotated synchronously to bring two arms up underneath a single bag segment on the input conveyor then carry it up and over, inverting it and depositing it on a stack immediately downstream.
This stack is formed as described in German patent document 3,138,221 of R.F. Bin (based on a Belgian priority of 16 Sep 1980) atop a belt or chain conveyor which is provided with stacking pins on which the bags are impaled. The conveyor moves in steps so that the stacking operation must be interrupted each time the stack is carried downstream to the punching machine. Thus each time the stack is carried away the upstream stacker must miss one cycle, or even two cycles when its cycling speed is high compared to the cycle speed of the conveyor.
Another disadvantage of this known machine is that it can normally only operate on machines which produce dual head-to-head bags. It cannot be adapted to the manufacture of standard separate handled-typed shopping bags, that is with a sack body from the top edge of which extend two parallel loop handles. Furthermore this known machine and most of the other standard such machines require continuous operator supervision of and/or intervention in the process.
The following U.S. patents are commonly owned with the present case and relate to bag making and stacking: U.S. Pat. Nos. 4,631,047, 4,695,346, 4,614,472, 4,512,757, 4,552,551, and 4,536,174